Calculation of the radiated sound field from a fluid-loaded plate with periodic structural discontinuities
Many periodic structures are subjected to forcing by a propagating pressure field. Examples include incident sound fields reflected off submerged ribbed hulls, and interior noise radiated from aircraft fuselages forced by an external turbulent boundary layer. The exact solution for a fluid-loaded infinite plate with periodic discontinuities is derived. Results of a systematic study are presented to characterize the intensity and directivity of the acoustic field radiated from the plate being forced by a propagating pressure field. The presence of structural discontinuities broadens the wavenumber spectrum of the structural response, causing there to be both supersonic (radiating) and subsonic (non-radiating) waves on the structure, even when the forcing wave speed is subsonic. It is also important whether the basic flexural wave speed of the plate is subsonic or supersonic. Particular attention is given to the interesting case of subsonic forcing on the subsonic structure, as a model of interaction between structure and turbulent boundary layer. The results provide physical understanding of the acoustic behavior of flexible surfaces with periodic discontinuities in terms of their reflection, transmission, and radiation properties.
